The invention relates to a magnetic valve with electronic control.
The magnetic valve has an energizing coil through which an energizing current passes via a closed switch of the electronic control. The electronic control also includes a maintenance phase which supplies the energizing coil with a maintenance current. The maintenance current is reduced with respect to the energizing current, and this is accomplished via a compensating resistor arranged parallel to the switch, with the switch in this instance being open.
Magnetic valves with electronic control of this kind are known from German Offenlegunsschrift (laid open application) No. 24 02 083. In these magnetic valves, an increased current is briefly directed through the energizing coil of the valve in order to increase the attractive force applied to the valve armature. In order to overcome the mass inertia of the moving parts of the magnetic valve and the spring force of the restoring spring which is normally provided, a substantially higher level of energy is required than is needed to maintain the valve in its switched-on or open state.
Also, the electrical current requirement for rapid and sure attraction of the armature of the magnetic valve is still further increased by the fact that the inductance of the energizing coil is substantially smaller when the armature is at rest (valve closed) than when it is not (valve open). Thus, because of the brief increase in the electrical current directed through the energizing coil, the maintenance current may be selected to be substantially smaller. Consequently, heating of the magnetic valve may be kept below the permissible upper limit, even when the valve is switched on for long periods. This permissible upper limit is frequently approximately 80.degree. C.
A further advantage of this feature is in that as a result of the increase in the force of attraction thus attained, the switching behavior of the magnetic valve is improved as well. In particular, shorter switching times can be attained.
In the magnetic valve of the German Offenlegungsschrift No. 24 02 083 already mentioned, the compensating resistor is bridged by a semiconductor switching triode or a cold conductor. The semiconductor switching triode is controlled in accordance with the induction of the energizing coil. In the attracting phase of the magnetic valve, the semiconductor switching triode is in a conductive state and therefore short-circuits the compensating resistor. If the magnetic valve has attained its working or open state, then, as a result of an increase in the induction of the energizing coil, the semiconductor switching triode is blocked. Thus, on account of the compensating resistor, a low-level current flows through the energizing coil, which is sufficient to hold the magnetic valve in its working position.
An alternating current is required as the operating current for actuating the magnetic valve. The use of the known magnetic valve is thus restricted, because of the mode of operation of the control electronics, to operation with alternating current.
Magnetic valves with electronic control for increasing the attractive output are also known in which a controllable rectifier is located in series with the energizing coil. The instant of ignition of the controllable rectifier is varied by a phase intersection control means in such a fashion that during the attracting phase, the ignition occurs sooner, and during the maintenance phase, the ignition occurs later. This known apparatus, disclosed in the German Offenlegungsschrift (laid open application) No. 25 11 564 or No. 20 23 108, for example, also has the disadvantage in that an alternating current or a pulsating direct current is required, or else a supplementary timing generator is required.